Primary diffuse leptomeningeal oligodendrogliomatosis is a rare malignancy of central nervous system without evidence of a primary intraparenchymal focus. We present a 25-year-old woman with the postmortem diagnosis of primary diffuse leptomeningeal oligodendrogliomatosis. She was paraplegic and had sensory loss at the level of thoracal 8-9 for nearly 15 months. There was no symptom due to increased intracranial pressure. Unexpectedly she died just before biopsy. Autopsy revealed a nodular lesion at the level of thoracal 10 vertebra and diffuse oligodendroglioma throughout the leptomeninges of the brain and spine without intraaxial focus. To our knowledge, this is the first case of primary diffuse leptomeningeal oligodendrogliomatosis causing sudden death in the literature.